This invention relates to a non-contact rotary signal generator for ON-OFF operation of an ignition system for the internal combustion engine and particularly a semi-conductor ignition system of the type so-called as the current-breaking type or the induced-energy accumulating type.
Generally, the semi-conductor ignition system of the aforementioned type becomes ON mode when the output voltage of the signal generator comes over the predetermined value V.sub.on and falls into OFF mode when the output voltage goes down to a value V.sub.off which is in a level lower than V.sub.on. Accordingly, once the ignition system becomes ON mode, it is required that the output voltage of the signal generator is maintained in a level exceeding V.sub.off until the commencement of OFF cycle defined by the internal combustion engine.
The principles and structures with disadvantages or inconveniences of the conventional signal generators to be used for the foregoing purpose will be appreciated from the following description prepared with reference to FIGS. 1 to 10 for convenience in understanding.
FIG. 1 shows a circuit diagram of a typical semi-conductor ignition system of the type so-called as the current breaking type or the induced energy accumulating type adapted to a four-cycle, straight two-cylinder type internal combustion engine in which the conventional signal generator is incorporated. This semi-conductor ignition system actuates in association with the output voltage of the non-contact signal generator SG. As shown in FIG. 4a, when the output voltage of the signal generator exceeds the value V.sub.on, the power transistor Q.sub.1 is switched into ON state through the amplifying stage A so as to close the circuit including the battery E, the primary winding of the ignition coil IGC and the power transistor Q.sub.1 and consequently the primary current i.sub.1 flows, as shown in FIG. 4b, through the closed circuit, the magnitude of which is predominantly defined by the battery voltage E.sub.B and the impedance of the primary circuit of the ignition coil. When the output voltage of the signal generator lowers to V.sub.off, the power transistor Q.sub.1 falls into OFF state to break the current. At the instance when the power transistor is changed into OFF state, the induced energy of 1/2L.sub.1 I.sup.2.sub.1C is accumulated in the ignition coil, wherein I.sub.1C is the primary current of the ignition coil of the instance and L.sub.1 is the reactance of the primary winding of the ignition coil. Due to the change of the power transistor Q.sub.1 into OFF state, the induced energy is transferred to the secondary winding which has a number of turns generally 100 times more than that of the primary winding, so that an extremely high voltage is generated to discharge across the electrodes of the ignition plug for igniting the fuel-air mixture gas filled in the combustion chamber. The ignition timing is intrinsic to the respective internal combustion engine for a purpose of increasing the fuel efficiency and is required to advance from the instant when the piston reaches the top-dead by a specific value defined by the revolution number per unit time center and the concentration of the mixture-gas.
FIG. 2 shows the conventional non-contact signal generator of the semi-conductor ignition system which generates a conduction pulse for each revolution of the internal combustion engine, as is required in a four-cycle, straight two-cylinder engine. The non-contact signal generator is of the so-called permanent magnet excitation-variable magnetic reluctance type and includes a stationary portion and a rotary portion. The rotary portion 6 revolves in synchronization with the crank-shaft of the engine. The reference numerals 61 and 62 designate a shaft and a rotary pole, respectively. The stationary portion is essentially comprised of a permanent magnet 4, a connecting member 2, a stationary pole 1, a pick-up coil 3 and a base 5 (or a lower yoke). In this combustion, since a conduction pulse is required for each revolution, a single stationary pole 1 and a single pick-up coil 3 are required and hence the so-called number of pole is one.
In the non-contact signal generator, the turning angle .theta. is defined as zero when the protruded end 65 of the rotary pole 62 is aligned to the stationary pole 1. At this time, the flux .phi. passing through the pick-up coil 3 and defined by the electromotive force of the permanent magnet 4 and the total magnetic reluctance through the magnetic circuit is maximized. In this position, the rotary pole 62 is commenced to turn. For the convenience of explanation, the rotary pole 62 turns clockwise around the shaft when seen from the shaft end to which the rotary pole is mounted. The gap length between the stationary pole 1 and the rotary pole 62 is varied in accordance with the rotation of the rotary pole 62 and the variation of the magnetic reluctance Rg of the gap is illustrated in FIG. 5a. As Rg is predominant in the total reluctance Rm of the magnetic circuit formed by the parmanent magnet, Rg may be considered to represent Rm. The flux .phi. passing through the pick-up coil 3 is varied with Rg as shown in FIG. 5b.
The electromotive force v produced in the pick-up coil 3 is defined as (d.phi./dt)=(d.phi./d.theta.).multidot.(d.theta./dt) and hence represented by the wave form shown in FIG. 5c since the angular velocity d.theta./dt is considered constant. This wave form coincides with the voltage wave form of the non-contact signal generator shown in FIG. 3 and FIG. 4a. Since the minimum radius portion 67 is positioned just opposite to the protruded end as shown in FIG. 2, the gap length or the magnetic reluctance Rg of the gap is maximized when .theta.=180.degree. as shown in FIG. 5a. Further, the configuration of the rotary pole is selected so that the magnetic reluctance Rg and the flux .phi. passing through the pick-up coil are symmetric when .theta.=0.degree. (360.degree. . . . ) and .theta.=180.degree. (540.degree. . . . ), for which reason the conduction time rate or the ratio of the conduction period of the primary current in the ignition coil to one cycle as shown in FIG. 4b is approximately 50% in case of high speed operation when the ratio between V.sub.on and the output voltage of the signal generator is reduced. The conventional system has no defect as far as the pole number is one notwithstanding serious disadvantages are caused in case the pole number is equal to or more than two.
FIG. 6 shows a circuit diagram of a semi-conductor ignition system of the current-breaking type or the induced energy accumulating type adapted for four-cycle, straight four-cylinder engine. It will be appreciated that the circuit of FIG. 6 includes two sets of the semi-conductor ignition system shown in FIG. 1 and the respective parts of the added set are designated by the primed reference numerals. The semi-conductor ignition system shown in FIG. 6 is controlled by the output voltage of the prior non-contact signal generator shown in FIGS. 7a and 7b. Since two sets of the ignition system are usually required to generate a high voltage alternately in the four-cycle, straight four-cylinder engine, the non-contact signal generator is required to generate an output voltage or responding to such the high voltage. For this purpose, the conventional signal generator includes two sets of the stationary poles with the pick-up coils which alternately produce an ignition signal voltage responding to the rotation of a single rotary pole. Each set of the stationary pole with the pick-up coil works similarly as the signal generator of a single pole shown in FIGS. 2a, 2b and 5. In FIGS. 7a and 7b, each part of the added set corresponding to the similar part of FIGS. 2a and 2b is designated by the primed reference numeral. FIG. 8 illustrates the operation of the conventional ignition system of the permanent magnet excitation-variable magnetic reluctance type with two poles. The turning angle .theta. is defined as zero when the protruded end of the rotary pole 62 is aligned to the stationary pole 1. At this time, the flux .phi..sub.1 passing through the pick-up coil 3 is maximized, the value of which is a little reduced than that of the signal generator with a single pole shown by dotted line in FIG. 8b due to the presence of the stationary pole 1. In accordance with the rotation of the rotary pole 62, the gap length between the stationary pole 1 and the rotary pole 62 is varied and maximized when .theta.=180.degree., where the magnetic reluctance Rg.sub.1 of the gap G is also maximized as shown in FIG. 8a.
The flux .phi..sub.1 passing through the pick-up coil 3 is remarkably reduced than that of a single pole because of two reasons described later. In this position, the protruded end 65 is aligned with the stationary pole 1' and the magnetic reluctance Rg.sub.2 of the gap G' on the side of the stationary pole 1' is minimized, which is concerned to the first reason. Seen from the permanent magnet 4, the magnetic circuits 1 and 1' are parallel. Generally, when a plurality of magnetic reluctances are connected in parallel, the magnetic reluctance for the permanent magnet is governed by one of less value. This phenomenon is clearly shown when .theta.=180.degree. in FIG. 8a. The second reason is the combination of a plurality of the stationary poles and the single rotary pole. Since the flux of the stationary pole 1' is maximized in case .theta.=180.degree. as shown in FIG. 8a, the magnetic potential difference developed in the rotary pole 62 is maximized and thus the flux of the stationary pole 1 is further reduced. As hereinbefore described, the electromotive force generated in the pick-up coil 3 is proportional to d.phi./d.theta. by separately considering d.theta./dt as shown in FIG. 8c in which the wave form is rather same as that of the single pole when .theta.=0.degree. but in the vicinity of .theta.=180.degree. the curve (solid line) of the two pole is considerably apart from that (broken line) of the single pole. This is caused by the large drop of .phi..sub.1 in this area, for which reason, a minor wave form is superposed on that of the single pole and dented portions of the electromotive force curve, as indicated by an arrow in the drawing are produced. The superposed minor wave form is called "interference voltage", the presence of which constitutes serious problems in the conventional system.
The stationary pole 1' shows the same phenomenon delaying in 180.degree. than the pole 1. In the operation of the semi-conductor ignition system including the interference voltage as shown in FIG. 9, the ON period of the power transistor as well as the period when the primary current of the ignition coil flows is twice produced in one cycle, which is followed by twice ignitions in one cycle. Since the first ignition precedes remarkably than the normal second ignition, the abnormal ignition is caused with various disadvantages such as lowering of the combustion efficiency and the generation of knocking.
The signal generator with three poles entails the similar problem except that the interference voltage arises in every 120.degree. of the turning angle .theta..
The above-mentioned signal generator of the type as hereinbefore described has a conduction time rate of 50%. Namely, the ratio of the conduction period for the primary current in the ignition coil relative to one cycle is 50%. Since the ignition capacity of the semi-conductor ignition system of the current breaking type or the induced-current accumulating type in the technical field of the invention is represented by the induced energy 1/2L.sub.1 I.sub.1C.sup.2 accumulated in the ignition coil, the conduction time rate may not be 50% as far as the value of 1/2L.sub.1 I.sub.1C.sup.2 is equivalent, for which reason an ignition system with a conduction time rate of less than 50% is employed in the commercial application. An illustration of this is shown in FIGS. 10a, 10b and 10c. Reduction of the conduction time rate is performed by merely varying the shape of the rotary pole with the same stationary portion. An example is illustrated in FIG. 10a. In case of the signal generator with the conduction time rate of 50% (FIGS. 4a and 7a), the minimum radius portion 67 of the rotary pole 62 only presents in a single point just opposite to the protruded end. In FIG. 10a, the minimum radius portion 67 extends in an angular range of 140.degree.. In the region of 140.degree., the magnetic reluctance Rg of the gap is never varied and hence the output voltage is remained zero or negligible if presents as shown in FIG. 10b. When the interference voltage hereinbefore described is superposed, the curve varies as shown in FIG. 10c in case of the signal generator with two poles. In this case, the following problem is also caused in addition to the double ignitions. Namely, when the value of the dented portion of the output voltage as indicated by an arrow in FIG. 10c comes over a value V.sub.off which is caused in a range of the highest speed and its vicinity, the conduction time rate approaches to 50%, which is accompanied by overheating of the ignition coil designed for the conduction time rate of 30%.